Treatment of thrombotic or atherosclerotic lesions in blood vessels using the endovascular approach has recently been proven to be an effective and reliable alternative to surgical intervention in selected patients. For example, directional atherectomy and percutaneous translumenal coronary angioplasty (PTCA) with or without stent deployment are useful in treating patients with coronary occlusion. These endovascular techniques have also proven useful in treating other vascular lesions in, for example, carotid artery stenosis, peripheral arterial occlusive disease (especially the aorta, the iliac artery, and the femoral artery), renal artery stenosis caused by atherosclerosis or fibromuscular disease, superior vena cava syndrome, and occlusion iliac vein thrombosis resistant to thrombolysis.
It is well recognized that one of the complications associated with endovascular techniques is the dislodgment of embolic materials which can occur during manipulation of the vessel, thereby causing occlusion of the narrower vessels downstream and ischemia or infarct of the organ which the vessel supplies. There are a number of devices designed to provide blood filtering for entrapment of vascular emboli in arteries. These devices have also been placed prophylactically, e.g., in the inferior vena cava, for prevention of pulmonary embolism in patients with a propensity for thromboembolism.
Filters mounted to the distal end of guidewires have been proposed for intravascular blood filtration. A majority of these devices includes a filter which is attached to a guidewire and is mechanically actuated via struts or a pre-shaped basket which deploys in the vessel. These filters are typically mesh “parachutes” which are attached to the shaft of the wire at the distal end and to wire struts which extend outward in a radial direction on the proximal end. The radial struts open the proximal end of the filter to the wall of the vessel. Blood flowing through the vessel is forced through the mesh thereby capturing embolic material in the filter.
One of the major disadvantages of present filtering devices is that the maximal expansion diameters of the deployed filters are fixed and sometimes fail to optimally and uniformly engage the vascular wall. An operator can only estimate the diameter of the vessel of interest and choose the filter accordingly. If the vessel, e.g., the aorta, is significantly affected by atherosclosis, the actual luminal diameter of the vessel would be over-estimated. In addition to blood filtering devices, this problem is also recognized for deployment of other medical devices, e.g., stents and occluders.
What is needed are simple and safe devices which facilitate placement of other medical devices in a body cavity, such as arteries and veins, and can be variably adjusted to ensure optimal placement of the medical devices. Existing devices are inadequate for this purpose.